Object counting apparatus



my, M. w

Dec; 1950 D. E. URRY 2,965,294

OBJECT COUNTING APPARATUS Filed Jan. 20, 1958 4 Sheets-Sheet 1 5cm 8 GEN.

SCAN

sen.

INJECTOR GATE MW DELAY J UNE EXTENDER COUNTER Dec. 20, 1960 D. E. URRY 2,965,294

OBJECT COUNTING APPARATUS Filed Jan. 20, 1958 4 Sheets-Sheet 2 86 'V A l \A/ f m8? 82-i\ k} PEG 2 83 88 A i I i Dec. 20, 1960 D. E. URRY OBJECT COUNTING APPARATUS 4 Sheets-Sheet 3 Filed Jan. 20, 1958 A B C FIG. 4.

Dec. 20, 1960 D. E. URRY OBJECT COUNTING APPARATUS 4 Sheets-Sheet 4 Filed Jan. 20, 1.958

FIG. 5.

FIG. 6.

OBJECT COUNTING APPARATUS Denis Edward Urry, Forest Hill, London, England, assignor to Rank Cintel Limited, London, England Filed Jan. 20, 1958, Ser. No. 710,059

Claims priority, application Great Britain Jan. 23, 1957 6 Claims. (Cl. 23592) The present invention relates to object counting apparatus, that is, to apparatus in which electrical signals developed as a scanning element is traversed in successive adjacent lines over a field containing particles to be counted are compared so that signals developed by a single particle may be associated and a single count only recorded in respect of each particle. Apparatus to which the present invention relates further includes means for sorting signals derived by scanning the particles into classes which are determined by a test as to whether or not their duration exceeds a predetermined time and are thus dependent upon the sizes of the particles from which the signals are derived.

In one known form of apparatus for carrying out these operations only those portions of a signal derived by scanning a particle which exceed a predetermined duration are applied to the means for associating all signals derived from a single particle. It has been found that this arrangement suffers from the disadvantage that some of the remnant signal portions may be of too short duration to produce full operation of the associating apparatus, with the result that mis-counting may occur.

In a co-pending application of Thomas C. Nuttall and Denis E. Urry, Serial No. 684,927, filed September 25, 1956, now Patent No. 2,891,722, and assigned to the same assignee as the present application it has been explained that this disadvantage may be overcome by artificially extending the duration of all residual signals so that their duration must be sufiicient to produce correct operation of the counting equipment. This is especially prone to occur when the method described in the above-mentioned application is employed.

It is an object of the present invention to provide object counting apparatus in which incorrect operation due to close proximity of individual objects is reduced.

It is a further object of the present invention to provide object counting apparatus in which incorrect operation due to close proximity of some objects to the edge of the scanned field is reduced.

Apparatus according to the present invention for determining the number of objects in a predetermined size range contained in a plurality of objects dispersed over a field comprises scanner means for generating a beam of energy for which the reflecting or absorbing properties of said objects differ from those of said field and for causing said beam to be focused upon an area of said field less than the area of any object in said predetermined size range and to scansaid field in a pattern of lines so spaced that any object in said size range must be traversed by at least one of said lines. Detector means are placed to respond to variations in the energy of said beam after modification by said objects by producing an electric signal varying in like manner as said energy. The signal from said detector means is applied to circuit means for producing therefrom a quantized signal having a first value when not less than a predetermined portion of the energy in said beam is not incident upon saidfield and a second value at all other times. This quantized signal is applied to circuit means operable between a first condition in which it provides an output signal having a first value and a second condition in which it provides an output signal having a second value, so that said bistable circuit is operable from said first to said second condition by transitions in said quantized signal from said first to said second value'and is operable from said second to said first value by transitions in said quantized signal from said second to said first value only when a predetermined interval has elapsed since said circuit means was operated from said first to said second condition. The output signals developed by said circuit means are applied to counter means which responds by providing an indication of the number of said objects within a predetermined size range.

A preferred circuit means for carrying out the invention includes a bistable circuit operable between a first condition in which it provides output and control signals individually having first values and a second condition in which it provides output and control signals individually having second values. The control signals developed by said bistable circuit are applied to control pulse generator means arranged to generate pulses of predetermined duration when a transition occurs in said control signal from said first to said second value. The pulse developed by the pulse generator is fed back to said bistable circuit means to cause it to remain in said second condition for the duration of said pulse. Thus any transition in the output signal developed by said bistable circuit from said first to said second value cannot be followed by a transition from said second to said first value during the time interval determined by the duration of said pulse. The output signals developed by said circuit are applied to the counter means.

The features of the invention which are believed to be novel are set forth with particularity in the appended claims. The invention itself, together with other objects and advantages thereof, may best be understood by reference to the accompanying description taken in conjunction with the accompanying drawings in which:

Figure 1 is a schematic diagram illustrating one embodiment of sizing apparatus for carrying out the present invention,

Figure 2 comprises a number of waveform diagrams illustrating the operation of part of the apparatus described in relation to Figure 1,

Fig. 2a is a diagram explanatory of the operation of the apparatus shown in Fig. 1,

Figure 3 is a diagram illustrating a field containing particles to be sized and showing thepath of a scanning element,

Figure 4 consists of a series of waveform diagrams showing the development of the difliculty which the present invention overcomes,

Figure 5 is a circuit digaram of one embodiment of apparatus suitable to be used as said circuit means, and

Figure 6 consists of a series of waveform diagrams used to explain the operation of the circuit shown in Figure 4.

The apparatus shown in Figure 1 comprises a cathode ray tube 1 which is supplied with appropriate heater current and e.h.t. voltage by power supply units 2 and 3. The electron beam produced in tube 1 is focused upon the luminescent screen 4 on the end of the bulb 5 by means of a suitable focusing device 6, conveniently an adjustable permanent-magnet device, and is deflected over screen 4 by magnetic fields developed in a deflection yoke '7 to which suitable currents are fed from scan generators 8 and 9 to cause the beam to scan an appropriate area on screen 4 in a pattern of closely spaced parallel lines.

The luminous pattern thus scanned on screen 4 of tube 1 is imaged by means of a suitable optical system, which as illustrated may comprise a lens 10, upon a field member 11 on which are dispersed particles such as 12 of which the number is to be determined. These objects must difler in some optical property for example, by being more opaque than the field which, in the apparatus illustrated is itself transparent. The size of the spot imaged onmember 11 must be sufiiciently small that it is less in diameter then the minimum dimension of the smallest objects to be counted. The pattern of lines in which the scanning spot traverses field 11 under the influence of scan generators 8, 9 must be such that an object of the minimum size to be counted will intercept at least one line. On the side of transparent field 11 remote from the objects is placed a light sensitive device 13 which may conveniently be a photo-electric cell. In an application in which objects to be sized are dispersed over an opaque field from which they differ in reflectance, photocell 13 would be exposed to light reflected from field 11. The current in cell 13 thus varies according as the scanning spot imaged from screen 4 of tube 1 is or is not incident upon one of objects 12, yielding in a preamplifier 14 to which photocell 13 is connected an electrical signal voltage varying in like manner as the illumination of cell 13.

The amplified signals appearing at the output of preamplifier 14, which may be omitted if a multiplier photocell is used as cell 13, are applied to a quantizer 15, which yields an output signal having one value when the scanning beam falls upon an object and another value when it does not. Thus quantizer 15 may comprise a bi-stable trigger circuit which changes from a first stable condition to a second when the input sign-a1 applied to it exceeds a first datum value and returns from the second to the first stable condition when the input signal falls below a second datum value slightly lower than the first datum. This action is illustrated by Figure 2 in which diagram 2A illustrates the passage of a scanning element 30 across objects 31 and 32 along the path indicated by broken lines 33, 34, diagram 23 shows the signal resulting from the scanning operation illustrated by diagram 2A, in which line 35 represents the variation of output voltage of amplifier 14 as spot 30-moves along its path and the trigger levels of quantizer 15 are indicated by broken lines 35 and 36', while line 38 in diagram 20 shows the variation of the output potential of quantizer 15.

The quantizedsignal from quantizer 15 then passes, in accordance with the present invention to a space stretcher 16, the function of which together with its manner of operation is described in more detail later in this specification. For the present it sutfices to say that the operation of space'stretcher 16 is such as to prevent inconveniently close proximity of its output signals however closely successive are the input signals which it receives from quantizer 15.

Output signals from stretcher 16 are then applied to sizing apparatus comprising a gate circuit 17, which may be any suitable known form of voltage-controlled signal gate, in such polarity that the gate is closed when the scanning element is not incident upon an object but opens to allow the passage of signals when the scanning ele- 'ment falls upon an object.

Injector 19 includes a circuit such that an output of predetermined magnitude is obtained when an input signal is received at either or both of two input terminals. Signals arising in injector 19 by reason of the application to it of either a shortened signal from clipper 18 or a delayed signal from delay device 19 are allowed to pass through gate 17 only if concurrent with a quantized signal. The signals which are allowed to pass through gate 17 are extended by extender 20, by a predetermined amount, that is, they are made to continue for a predetermined period, which for reasons explained below is conveniently made equal to two picture points, after their original termination. By the term picture point is meantthe period-of time required for the scanning element to traverse in the line direction a distance equal to that between the centers of adjacent scanning lines. The extended signals are then applied to delay device 21, which is arranged to delay the signals by a time not quite equal to the duration of one line scanning period. Most conveniently the delay introduced by delay device 21,

is made equal to one line scanning period less than one picture point, so that the delayed signal passes through injector 19 and its leading edge arrives at gate 17 one picture point before the end of a line scanning period subsequent to the initiation of the original shortened signal wrile its lagging edge, owing to the extension introduced by device 20, arrives one picture point late. During the scanning of any object of a size to be counted which intercepts more than one scanning line gate 17 will be open when the leading edge of the extended signal reaches it and the pulse will be recirculated, becomin progressively broader about its original mean position.

This action is illustrated in Figure 2a, in which the outline of an object being counted is represented by the heavy line 82. This object is considered as being traversed by a scanning element along each in turn of a succession of scanning lines represented by fine parallel lines, indicated generally by reference 85. The minimum size of object to be counted is that represented by dimension 84 as applied to the second of scanning lines 83 which encounters the object. This line is indicated specifically by reference 85. It will be seen that in line object 82 is slightly greater than the minimum dimensions and a shortened pulse is therefore emitted by clipper 18 and passed into the signal circulatory system via injector 19. Since gate 17 is opened by the presence of a quantized signal at the-output of stretcher 16 the pulse passes on to extender 20 to yield a pulse which commences at a time later than the leading edge of the quantized signal by said second predetermined amount equivalent to minimum dimensions 84 and continues after the trailing edge of the-quantized signalfora time determined by theamount added to the pulse duration by extender 20. Conveniently the additional pulse duration amounts to two picture points. The pulse leaving extender 20 is represented by the thickening at 85 of line 89.

During-the next line the circulating pulse arrives at injector 19 before the commencement of the shortened pulse derived during the scanning of that line and terminates after the shortened pulse finishes. The injector is arranged to provide an output-whenever -it receives either a quantizedor a circulated pulse, so that it providesan output pulse 87 which commences one picture point earlier than the pulse in the preceding line, as indicated by the broken line 86, which has a slope of 45.

This'action is repeated during successive scanning lines until, as indicated at 88 the beginning of the recirculated it was derived. Part-of-this extension will be removed bytheoperationofthe gate 17 whichcloses as thequantized pulse ends when the scanning spot leaves the object. This pulse is again extended by two picture points by the operation of extender 20 to yield a pulse, illustrated by bold line 87, which commences one picture point before the pulse derived in the preceding line and terminates two picture points after the scanning spot leaves the object and ends the quantized pulse. During the scanning of the rest of the object each circulating pulse will have the same duration as the intercept of the object in the currently scanned line plus two picture points.

There is thus produced at the terminals of a counter device 22 which should include means for delaying the output from delay device 21 by a further one picture point period a succession of signals which is continuous during the scanning of the object and will result in a single count only being recorded. The operation of apparatus according to the invention is thus distinguished from that of known apparatus in which a constant amount is slipped from each quantized signal and the resultant signals applied directly to a counter. If such a procedure were followed in the case illustrated in Figure 2a, two separate successions of pulses would be generated, separated by an interval corresponding to the waist of the object, which has intercepts less than the minimum size to be counted, with the result that two counts would be recorded. Thus pulses originated from any object in the size range to be counted and injected into the circulatory loop at device 19 will be recirculated as long as the scanning element encounters the same object in each successive line, the circulated clipped pulse becoming progressively broader about its original magnitude until it acquires the dimensions of the pulse applied to clipper 18.

Signals from either end of delay line 21 are applied to a counter 22, WillCil should include means for delaying the output from delay line 21 by a further one picture point interval. Counter 22 is of the type which includes anti-coincidence means such that a count is recorded only at the commencement, or at the end, of a succession of pulses occurring at exactly one-line intervals. Counter means of this kind has been described for example in US. Patent No. 2,803,406 assigned to the same assignees as the present application.

The operation of apparatus including gate 17, clipper 18, injector l9, extender 20, delay line 21 and counter 22 is to count only objects which give rise to at least one pulse having a duration greater than the predetermined duration set by the initial amounts suppressed by clipper 18 from each signal applied to it.

The operation of such systems, without the inclusion of stretcher 16 is generally accurate but, as has already been briefly mentioned, residual inaccuracies still arise when the interval between signals arising from successively scanned objects is very short. The occurrence of this defect is now further explained with reference to Figures 3 and 4 of the drawings.

In Figure 3 is shown part of a field containing opaque particles represented by shaded areas such as 41, 42, 43, 44 and bounded by a rectangular frame, parts of two sides of which are shown at 45, 56. The field is supposed to extend beyond the area illustrated where this is bounded by broken lines 47, 48. The field is scanned in successive adjacent lines by a scanning element which for convenience in illustration is shown as moving parallel to side 46 of the area. The tracks of the scanning element in three successively scanned lines are indicated by the shaded strips A, B and C.

In Figure 4 are shown three pairs of waveform diagrams representative of the conditions arising from the scanning of each of lines A, B and C of Figure 3. The upper diagram of each pair is intended to represent the quantized electrical signal developed by the passage of the scanning element along the correspondingly labelled line of Figure 3, while the lower diagrams, A, B, C represent the signal developed in subsequent apparatus as a result of the application to it of the quantized signals shown at A, B, C.

It is assumed that, as in the case in practice, the frequency response of the later apparatus is unavoidably less wide than that of the quantizing circuit. The effect of this degraded response will be described below. It will be seen that diagram A is a replica of diagram A. This is because the durations of all signal elements derived during the scanning of line A are greater than the minimum response of the equipment. Diagram B, however, is not identical with diagram B. This is because the distance between particles 42 and 43 in the direction of line B is very small and gives rise to a pulse 49 which is of shorter duration than the resolution of the subsequent equipment. As is shown by diagram B, the result is that particle 43 is expunged from the signal which is effective in the later apparatus. In line C, particle 42 is not encountered so that particle 43 gives rise to a normal signal again, as is shown in diagram 4C. The result of the incorrect excision of the particle 43 response in line B is therefore that this particle becomes efiective on the sizing equipment as two separate particles of different sizes, with a corresponding error in the count.

Line C also illustrates another and more common source of error in sizing equipment. Particle 44 has in this line approached so closely to the margin of the scanned area that the inadequate equipment response to pulses of brief duration causes the normal masking to be overridden and yields an incorrect signal level during the flyback interval subsequent to the scanning of line C. The result of this error in signal level is that when the true level is again restored in a subsequent line the effect upon the particle-identification circuits is the same as when another particle is encountered and a false count will be recorded. Where, as frequently occurs, a particle is closely adjacent to a margin in a large number of consecutive lines it is found that several false counts may be produced by one and the same particle.

The present invention overcomes this difiiculty by arranging that the duration of the signal interval resulting as the scanning element passes from a particle to an adjacent particle or to the boundary of the scanned field cannot be less than an amount which is sufiicient to ensure a correct response of the apparatus to which the signal is applied.

One form of apparatus suitable for this purpose is illustrated by the circuit diagram of Figure 5. In this figure, quantized signals developed as the scanning element traverses the particle-containing field are received at terminal 51 and thence pass to the grid of a bi-stable trigger circuit formed by cathode-coupled valves 52, 53. The bias potentials on the grids of this trigger circuit are so arranged that in the absence of the remainder of the circuit the signal arising at the anode of valve- 53 and applied to the output terminal 54 would be a replica of that received at terminal 51.

The signals received at terminal 51 comprise signals which have a more positive value corresponding with the traversal of the scanning element over a particle and a more negative value corresponding to the passage of the scanning element over the spaces between particles. Thus valve 52 is caused to pass current for particles and valves 53 to pass current for spaces. When the anode of valve 52 goes positive on the initial transient of a space, a positive-going spike is developed by a differentiating circuit comprising capacitor 55 and the resistance between the grid of a further valve 56 and the negative terminal of the anode supply. Capacitor 55 is connected to the grid of valve 56 by Way of a crystal diode 57 which passes positive-going impulses to the valve grid much more readily than-the negative-going impulses resulting from the terminal transients. The effect of these latter upon the operation of valve 56 is further reduced by a second crystal diode 58 which is connected between the grid .of valve 56 and earth in series with a capacitor 59.

The polarity of diode -58 is such that any negative-going signals are by-passed from the grid of valve 56. This grid is connected to the slider of a potentiometer 60 which is connected between resistors 61 and 62 across the HT. supply. Potentiometer 60 is so adjusted that valve 56 is normally cut-off but is caused to pass current when a positive-going signal is applied to it via diode 57. Valve 56 is coupled to a further valve 65 by a common cathode resistor 63 and a coupling capacitor 64 from the anode of valve 56 to the grid of valve 65, which grid is returned by way of'a resistor 66 to the HT. line so that valve 65 is normally conductive. Thus valves 56 and 65 form a known type of monostable trigger circuit in which the duration of the unstable condition in which valve 65 is cut oil is determined primarily by the values chosen for capacitor 64 and resistor 66 and secondarily by the potential to the grid of valve 56 from potentiometer 60. When the grid of valve 56 is made positive by the positivegoing signal applied to its grid at the beginning of a space, valve 65 is cut off by the negative-going signal applied to its grid from the anode of valve 56. The time for which this condition persists is arranged by suitable choice of circuit values to be equal to the minimum permissible duration of a space if imperfect operation of the subsequent sizing circuits is to be-avoided.

When valve 65 is cut off a positive-going pulse arises across itsanode resistor 67 and is fed by way of a cathode-follower valve 68 to the anode of a diode valve 73, the cathode of which is connected to the grid of valve 53. The grid of valve 68 is connected to a point of suitable potential, provided by resistors 69, 70 connected across the BLT. supply, by way of a diode 71 so poled as to block the passage of the positive-going signals applied to the grid of valve 68 from the anode of valve 65. Any negative-going signals appearing at the grid of valve 68 will pass through diode 71 and produce across a capacitor 72, connected from the diode anode to earth, a bias potential which ensures the correct operation of valve 68, if a rapidly recurrent train of pulses is applied to it, by DC. restoring the applied signal. While this positive pulse is applied to its grid, valve 53 is prevented from becoming non-conductive even though the signal applied to its grid from the anode of valve 52 should cease. Thus the negative-going signal at the anode of valve 7 53 which commences at the beginning of any space signal received at terminal 51 must persist until the end of the period determined by trigger 56, 65 or until theend of the space period of the applied signal, whichever is the longer. In this way it is ensured that no space signal which is too short to produce correct operation can be passed on to the sizing circuits.

The operation of the circuit is now further described with reference to Figure 6. In this figure, diagram D represents two space signals applied to terminal 51 of the apparatus illustrated in Figure 5. The left-hand signal 74 is represented as having a duration less than the permissible minimum, while the right-hand signal 75 is of substantially greater duration than this minimum. Diagram E illustrates the positive pulses arising at the grid of valve 56 as a result of the input signals shown in diagram D. Diagram F shows the positive-going pulses generated at the anode of valve 65 and applied by way'of cathode-follower 63 to the anode of valve 73. Diagram Gshows the resultant output signals passed to terminal 54. It will be seen that the output signal resulting frorn'input signal 74 has a duration determined by the trigger circuit 56, 65 while the output signal resulting from input signal 75 has the same duration as that signal, Lclaim:

1. In apparatus for determining the number of objects in a predetermined size range contained in a plurality of objects dispersed over a field, scanner means for generating abeam of energy for which thereilecting or absorbing properties of said'objccts dilfer from those of said field and for-causing said beam to be focusedupon an area of said .field less than the .area of any object in said predetermined size range and to scan said field in a pattern of lines so spaced that .any object in said size range must be traversed by at least one of said lines, detector means responsive to variations in the energy of said beam after modification by said objects to produce an electrical signal varying in like manner as said energy, circuit means responsive to said signal for producing therefrom a quantized signal having a first value when not less than a predetermined portion of the energy in saidbeam is not incident upon said field and a second value at all other times, circuit means arranged to pro vide an output signal having a first value when said circuit is in a first stable condition and a second value when in a second stable condition, said circuit means being operable from said first to said second condition by applied signals at all times when in said first condition but operable from said second condition to said first conditionby the cessation of said applied signals only after the expiration of a predetermined interval after being operated from said first to said second condition, counter means responsive to a succession of pulse signals of varying duration by providing an indication of the number of said pulses within a predetermined range of duration and meansfor applying said output signals to said counter means.

2. Apparatus constructed in accordance with claim 1 for. determining the number of objects in a predetermined size range in which said circuit means comprises bistable circuit means operable by applied signals between a first condition in which it provides output and control si nals individually having first values and a second condition in which it provides output and control signals individually having second values, means for applying said quantized signal to operate said bistable circuit so that transitions in said quantized signal from said first to said second value operate said bistable circuit from said first to said second condition and transitions in said quantized signal from said second to said first value tend to operate said bistable circuit from said second to said first condition, pulse generator means triggered by applied signals to develop a pulse of predetermined duration, means for applying said control signal to said pulse generator so that transitions in said control signal from said first to said second value initiate the development of said pulse and means for applying said pulse to said bistable circuit to cause said bistable circuit to remain in said second condition during theexistence of said pulse.

3. Apparatus constructed in accordance with claim 1 for determining the number of objects in a predetermined size range in which said scanner means comprises means for generating a beam of light, means for focusing said beam of light upon an area of said'field less than the area of any object in said predetermined size range and means for scanning said beam of light over said field in a pattern of lines so spaced that any object in said size range must be traversedby at least one of said lines and said detector means comprises electrically light-sensitive means exposed to light from said field to produce an electrical signal varying in magnitudeaccording as saidbeam is or is not incident upon an object.

4. Apparatusconstructed in accordance withclaim 3 for determining the number of objects in a predetermined .size range in which said scanner means comprises a cathode ray tube including electron gunmeans for developing a beam of electrons, and for projecting said electrons upon a luminescent screen, means for focusing said electrons in a, spotupon said screenand forv deflecting said ,beam so that said spot traverses said screen in apattern .of closelyspaced' lines and. means for imaging light emitted by said screen under bombardment, by said electrons ,in the plane of said field.

5. Apparatus. constructed in accordancewith claim 3 for determining the. number of objects in a predetermined size range contained among a number of objects dispersed over a field more transparent than the objects, in which said detector means comprises a photocell exposed to light from said scanner means which passes through said field.

6. Apparatus constructed in accordance with claim 3 for determining the number of objects in a predetermined size range contained among a number of objects dispersed References Cited in the file of this patent UNITED STATES PATENTS Hillier Jan. 10, 1950 Sandorff et al. Jan. 29, 1952 

